Manufacture of drawn thermoplastic fibrillary products

ABSTRACT

A PROCESS FOR DRAWING A THERMOPLASTIC FIBRILLARY PRODUCT WHICH PROMISES THE STEPS OF FEED ING THE FIBRILLARY PRODUCT TO A DRAWING ZONE; DRAWING THE PRODUCT IN THE DRAWING ZONE, THERE BEING A MAXIMUM CHANGE IN THE DENIER OF THE PRODUCT AT THE DRAWING POINT IN THE DRAWING ZONE; PASSING THE FIBRILLARY PRODUCTG IN SLIPPING CONTACT OVER AT LEAST ONE FRICTION MEMBER AFTER THE DRAWING POINT AND IN THE DRAWING ZONE; AND THEREAFTER DISCHARGING THE PRODUCT FROM THE DRAWING ZONE. ALSO APPARATUS FOR CARRYING OUT THE PROCESS AND THE DRAWN PRODUCT ARE DISCLOSED.

April 11, 1972 I SEMPEL E'IAL 3,655,839

MAAUFACTURE OF DRAWN THERMOPLASTIC FIBRILLARY PRODUCTS Filed Oct. 2, 1969 F/GI 2.

INVENTORS HENDRINUS SEMPEL 8 HENDRIK POTMAN BYW%%A RNEY Patented Apr. 11, 1972 3,655,839 MANUFACTURE OF DRAWN THERMOPLASTIC FIBRILLARY PRODUCTS Hendrinus Sempel and Hendrik Potman, Arnhem, Netherlands, assignors to Akzona Incorporated, Asheville, N.C. Filed Oct. 2, 1969, Ser. No. 863,180 Claims priority, application Netherlands, Oct. 8, 1968, 6814352 Int. Cl. B29c 17/02 U.S. Cl. 264-40 2 Claims ABSTRACT OF THE DISCLOSURE A process for drawing a thermoplastic fibrillary product which comprises the steps of feeding the fibrillary product to a drawing zone; drawing the product in the drawing zone, there being a maximum change in the denier of the product at the drawing point in the drawing zone; passing the fibrillary product in slipping contact over at least one friction member after the drawing point and in the drawing zone; and thereafter discharging the product from the drawing zone. Also apparatus for carrying out the process and the drawn product are disclosed.

This invention relates to a process for drawing of a thermoplastic fibrillary product in which the product is drawn and is passed in slipping contact over a friction member in a drawing zone under such conditions that product breakage is reduced and to the drawn fibrillary product produced thereby.

In a known process of this type for effecting a two-stage draw of a yarn of polyethylene terephthalate (which is described in US. Pat. 2,611,923), the yarn successively passes over a feed roll, a heated first draw roll and a second draw roll. The yarn makes several wraps around each of the draw rolls to prevent slippage between the yarn and the roll. The drawing point for the first draw as well as that for the second draw lie on the first draw roll. It has been found that many yarn breakages occur in this known process.

Advantageously, this invention provides a drawing process that substantially reduces the occurrence of breaks in the fibrillary product. Thus, the invention contemplates a process for drawing a thermoplastic fibrillary product which comprises feeding the fibrillary product to a drawing zone, drawing the product in the drawing zone and discharging the product from the drawing zone; the product being passed in slipping contact over at least one friction member in the drawing zone after the product has moved through the drawing point. The term drawing point is to be understood as referring to that point of the drawing zone through which the product moves at which there is a maximum change in denier. The friction member acts as if it were as a separating member, between successive drawing zones, but unlike the known separating member, such as the first draw roll of the known process, it does not impose a certain speed on the product. Nevertheless, just like known separating members, the friction member acts as a tensioning member which brings about a change in the tensile force prevailing in the fibrillary product. The magnitude and the sign or direction of this change in tensile force are dependent, inter alia, on the relative speed of the product and the friction member on which it slips, and the surface condition of the member. The optimum relative speed of the draw roll may be determined experimentally.

The friction member may be rotary or stationary. Both constructions have certain particular advantages. In the case of a rotary friction member, the tensile force may also be influenced by the speed of the friction member.

A stationary friction member has the advantage of a simpler construction.

With the stationary construction use may with advantage be made of a drawing process characterized in that a liquid is passed through the inside of the friction member for controlling its temperature.

Moreover, with this process a stationary friction member has the advantage that it does not present any sealing problems encountered with the transport of liquid through a rotary member.

For thread-shaped, ribbon-shaped, or the like fibrillary products with which the drawing is attended with a strong development of heat at the drawing point, as is the case at high-speed drawing and with relatively heavy-denier yarns, it is particularly advantageous to employ a drawing process in which a cooling liquid is passed through the inside of the friction member. This applies particularly to the drawing of polyamide yarn.

However, aside from being used for withdrawing of excess heat, the liquid may also be employed for transporting heat to the friction member. This is of importance if the member is to be heated to a temperature higher than that resulting exclusively from the drawing and frictional heat generating within the fibrillary product. This may be the case, for instance, when drawing yarns that entirely or partly consist of polyethylene terephthalate.

It will be appreciated that the drawing process according to the invention may with advantage be used in spindrawing of yarns, threads and the like fibrillary products.

In general, the process of this invention may be employed for the drawing of synthetic linear polymerization products. Favorable results have been obtained in the drawing of linear polyesters, particularly polyethylene terephthalate, and linear polyamides, particularly polyepsiloncaprolactam.

A particular embodiment of the process of this invention comprises feeding a synthetic thread to a driven feed roll, subjecting the thread to a first draw, passing the thread from the feed roll to at least one friction member over which the thread slips, subjecting the thread to a second draw, passing the thread from the friction member to a draw roll which is driven at a circumferential speed that is higher than that of the feed roll, and discharging the drawn thread.

Yet another embodiment of the process of this invention is characterized in that the first draw begins on the feed roll. Advantageously, it has been found that by this embodiment, drawing is attended with still fewer breakages.

High speeds, particularly those occurring in spindrawing, form an obstacle in the use of a drawpin for localizing the drawing point, because its use leads to many thread breakages. If one desires to locate the drawing point without applying a drawpin between the feed and draw ro1l(s), then it is advantageous to employ an embodiment of the process characterized in that the drawing point is localized by measuring the temperature of the thread or ribbon-shaped product at the point where the drawing point is desired to be positioned. When the drawing point moves away from its desired position, one or more process parameters that affect the position of the drawing point are, on the basis of this temperature measurement, changed to cause the drawing point to return to its desired position.

A very suitable embodiment of the process for drawing synthetic fibrillary products is characterized in that before the temperature of the product is measured, the product is passed through a heated zone, and the temperature of the heated zone serves as a process parameter by which the position of the drawing point is changed.

Yet another embodiment of the process of this invention for use in the spindrawing of polyethylene terephthalate yarn, is characterized in that the yarn is supplied to a driven, heated feed roll and then to a friction member which is heated to a temperature which is higher than that of the feed roll.

It is preferred that in this embodiment of this process the feed roll should be heated to a temperature in the range of from 65 C. to 90 C., and the friction member to a temperature in the range of from 180 to 225 C. The most favorable results are found to be obtained at a feed roll temperature of approximately 85 C.

This invention is also concerned with utilization of apparatus for carrying out the heretofore described process for drawing of a thermoplastic thread-shaped, ribbon-shaped product or like fibrillary product, which comprises at least one feed roll for supplying a thread to be drawn, at least one draw roll that can be driven at a circumferential speed which is higher than that of the feed roll, and a friction member provided between the drawing point and the drawing roll which allows slippage of the thread. It will be understood that the term friction member as used herein defines a driven or stationary roll (or rolls) or a pin.

For the purpose of enhancing the occurrance of slippage it is recommended that use should be made of a friction member having a matte chromium plated running surface.

In particular it has been found for carrying out that embodiment of the drawing process in which the first draw begins on the feed roll, it is preferred that use should be made of an apparatus with the feed roll having a matte chromium plated running surface.

A very suitable embodiment of the apparatus utilized is characterized in that at the position where drawing occurs, there are provided a temperature sensing element for measuring the temperature of the thread or ribbonshaped product and means cooperating with the temperature'sensing element for efiecting a change in the position of the drawing point to maintain the drawing point at a desired position.

A preferred embodiment of this apparatus utilized is characterized in that the means for changing the position of the drawing point comprise a heating device with the aid of which the temperature of the thread or ribbonshaped product can be changed before it passes the temperature sensing element and an automatic controller having its input connected to the temperature sensing element and its output connected to the heating device for localizing the drawing point adjacent to the position of the temperature sensing element.

Preferably, use is made of the heating device which is located within the feed roll.

Finally, this invention also is directed to a unique process for drawing a fibrillary product.

The invention will be further described with reference to the accompanying drawings, in which:

FIG. 1 shows an apparatus for use in the spindrawing of yarn of polyethylene terephthalate in accordance with this invention;

'FIG. 2 shows a detail of a portion of the apparatus shown in FIG. 1 having a modified yarn path; and

FIG. 3 shows an apparatus of the invention for use in the spindrawing of yarn of poly-epsiloncaprolactam (i.e., nylon-6).

On the drawing portion of the spindraw apparatus shown in FIG. 1, a yarn 1 of polyethylene terephthalate is successively drawn and wound. The yarn 1 which issues from a spinning apparatus (not shown), successively passes a feed roll 2 with a separator roll 3, a pair of rolls 4 and 5, a draw roll 6 with a separator roll 7, and a grooved drum 8, and is then wound into a package 9, driven at a constant circumferential speed by a friction roll 10. All the rolls are rotated by a driving mechanism (not shown). In order that the yarn may be drawn, the circumferential speed V of the pair of rolls 6, 7 is chosen to be higher than the circumferential speed V of the pair of rolls 2, 3. Both the pair of rolls 2, 3 and the pair of rolls 4, 5 are provided with heating devices having automatic temperature control. The pair of rolls 2, 3 are heated to a temperature T and the pair of rolls 4, 5 to a temperature T The process conditions are so chosen that the drawing of the yarn begins on the pair of rolls 2, 3, each of which are provided with matte chromium plated running surfaces. Each of the rolls 4, 5 also have matte chromium plated running surfaces. This roll pair (i.e., rolls 4, 5) are driven at a circumferential speed V: which is so chosen that slippage occurs between this pair of rolls and the yarn 1, so that the rolls 4, 5 do not impose a particular speed on the yarn. Instead, these rolls ensure that as a result of the friction acting on the yarn, a tension gradient occurs in the yarn, so that the total drawing section or zone is divided into two successive zones, namely a primary drawing zone and a secondary drawing zone.

FIG. 2 shows a modified yarn path for the apparatus of FIG. 1 in which the yarn 1 may make one full wrap or a plurality of wraps around the pair of rolls 4, 5 so that the angle of wrap around the rolls is larger than in the yarn arrangement shown in FIG. 1.

On the drawing portion of the spindraw apparatus shown in FIG. 3, a nylon yarn 1' is in a continuous process, drawn, allowed to relax, and wound. The yarn 1', which issues from a spinning apparatus (not shown) successively passes a driven, electrically heated feed roll 2' with separator roll 3, a thread guide 11 with built-in temperature sensing element, a driven roll 4', a driven and heated pair of rolls comprising a draw roll 6 and a separator roll 7, a driven pair of rolls 12, 13, and a grooved drum 8. The yarn .1 is then wound into a package 9, which is driven at a constant circumferential speed by a friction roll 10. The temperature sensing element in the thread guide 11 is connected to an automatic controller 14, which is connected to the electric heating source of the feed r0112.

The control loop thus obtained will ensure that the drawing point formed in the drawing process is localized at the thread guide 11. At the position of the drawing point the cross-sectional area of the yarn is greatly changed over a distance which is often relatively short. There occurs a so-called drawing neck, the formation of which may be attended with an appreciable increase in temperature due to the heat liberated upon the strong deformation in the neck.

Localization of the drawing neck is now effected in the following manner. When the neck is positioned between the feed roll 2' and the temperature sensing element in guide 11, and close to the temperature sensing element, then the element will register a high temperature for the yarn surface. The controller 14 responds thereto in that it reduces the heating of the feed roll 2'. To this end the electric heating device in roll 2' may be, for instance, entirely or partly switched off. The resulting fall in temperature of the feed roll 2' leads to a decrease of the yarn temperature, so that the drawing neck moves in the direction of the temperature sensing element. When the neck passes the temperature sensing element, the element registers a falling yarn temperature. As a result, the controller 14, in cooperation with the heating device of the feed roll 2', increases the temperature of the roll, so that the drawing neck will move in the opposite direction. In this Way the automatic control loop formed by the yarn, the temperature sensing element, the automatic controller and the heated feed roll, keeps the drawing neck in the desired position.

The roll 4 has a matte chromium plated running surface. Its circumferential speed is equal to that of the roll 2', so that the yarn 1' slips on the roll 4. Thus, prior to the roll 4 the yarn is already subjected to a primary draw, so that at the roll 4 its speed is higher than the circumferential speed of the rolls 2 and 4'.

The tension gradient caused by the roll 4' ensures that the drawing of the yarn takes place in two stages, the roll 4' acting as a separating member between the stages. The zone between the pairs of rolls 6, 7 and 12, 13 serves as relaxation zone.

The magnitude of the change in the tensile force brought about by the slip roll(s) 4 (and 4) is determined, inter alia, by the surface conditions of the roll, the angle of wrap around it and its temperature, the surface condition of the yarn and the relative speed of the roll and the yarn. If the difference between the yarn speed at the slip rolls, e.g. roll pair 4, 5 and the circumferential speed of the rolls is positive, then the tensile force on the yarn will increase as it passes over the slip rolls. If this difference is negative, then the reverse applies. This means that the circumferential speed of the slip roll (or rolls) may be used for setting the magnitude as well as the sign (i.e. positive or negative) of the change in the tensile force. The optimum circumferential speed of the slip roll may be determined empirically. The slip roll may also serve as heating or cooling element. It has the former function, i.e., heating in the apparatus of FIG. 1, and the latter, i.e., cooling, in that of FIG. 3. In general, the process according to the invention may be used for the drawing of organic thermoplastic materials, such as linear polyamides (e.g., nylon-6, nylon-6,6, and the like), and linear polyesters (e.g., polyethylene terephthalate, polypivalolactone, and the like).

The process of this invention will be further understood by reference to the following examples:

EXAMPLE I Using a spindrawing apparatus as shown in FIG. 1, a number of experimental runs were made with a 48- filament polyethylene terephthalate yarn which was drawn to an industrial yarn having a denier of 250.

In all the runs, the circumferential speed of the pair of rolls 2, 3 was 400 meters per minute, their temperature being 85 C. and the temperature of the pair of rolls 4, 5 was 220 C.

The following Table A shows the results obtained in these runs. The tenacity of the yarn is calculated on the denier of the yarn before the tensile test.

TABLE A Run 1 2 3 V1 (meters per minute) 400 400 400 400 V (meters per minute) 1, 760 1, 920 2, 090 2, 344 V (meters per minute) 2, 500 2, 480 2, 495 2, 480 Total draw ratio. 6. 25 6. 20 6. 24 6. 20

1 C.) 85 85 85 85 T2 C 220 220 220 220 Denier 244 248 234 250 Tenacity (grams per denier). 10. 6O 10. 55 10. 27 Elongation at break, percent 9.4 9. 4 10. 1

EXAMPLE 11 Using the same spindrawing apparatus and the same type of initial yarn described in Example I, a number of additional experimental runs were made, using the modified yarn path shown in FIG. 2. As can be seen from FIG. 2, in some cases the yarn now made one full wrap around the pair of rolls 4, 5, (in other cases the yarn made a plurality of wraps), so that the angle of wrap around the pair of rolls 4, 5 (in other cases the yarn shown in FIG. 1. The process ran considerably less well than it did under the conditions applied in Example I in that a relatively large number of breakages occurred. The maximum attainable draw ratio was 6.00. It will be appreciated that the yarn set-up shown in FIG. 2, particularly when the yarn makes a plurality of wraps around the rolls, reduces the occurrence of slippage between the yarn and the rolls and thus accounts for the increase in yarn breakage.

6 EXAMPLE 111 A further number of experimental runs were made for the purpose of establishing how the temperature of the pair of rolls 2, 3 affects the process of the invention. Here, just as in Example I, the yarn was passed over the pair of rolls 4, 5 while it was allowed to slip thereon. The results obtained are summarized in Table B.

TABLE B Run 1 2 3 4 5 6 V (meters per minute) 400 400 400 400 400 400 400 V2 (meters per minute) 2, 345 2, 090 2, 345 2, 090 2, 345 2, 090 2, 090 V (meters per minute) 2, 2, 485 2, 485 2,485 2, 485 2, 485 2, 485 Total drawratio 6. 20 6. 20 6. 20 6. 20 6. 20 6. 20 6. 20 65 65 75 75 85 85 220 220 220 220 220 220 220 241 246 249 250 244 241 248 Tenacity (grams per denier) 1, 034 946 946 973 1, 015 1, 026 981 Elongation at break,

percent 9. 7 9. 2 9. 3 9. 2 9. 8 9. 2 9. 0 Boiling water shrinkage, percent 8.0 8. 4 8. 0 8. 0 7. 9 7. 8 7. 9

It was found from these experimental runs that for the process to run smoothly the temperature T of the pair of rolls 2, 3 has to be lower than 95 C., because otherwise the number of yarn breaks would be too high. At a temperature of approximately 85 C. the number of breaks was found to be at a minimum.

EXAMPLE IV Using the apparatus shown in FIG. 3, a 140-filament nylon-6 yarn was drawn to an industrial yarn having a denier of 1260. The circumferential speeds of the rolls 2, 4' and 6, 7 and 12, 13 were, respectively, 400 meters per minute, 1920 meters per minute and 1880 meters per minute. The total draw ratio was 4.8. The pair of rolls 6, 7 were provided with a heating device for heating these rolls to a temperature of 220 C. The temperatures of the rolls 2, 4' and 12, 13, measured on the running surfaces, were, respectively, 40 to 45 C., C. and 100 C. The drawing neck was kept at the guide 11.

The drawn yarn was found to have a tenacity of 9 grams per denier, an elongation at break of 22%, and a boiling water shrinkage of 11%.

When the roll 4 was omitted, the draw ratio attained was as low as approximately 4.2.

It should be noted that the afore-mentioned results could be obtained with a separating roll 4 of which the circumferential speed is equal to that of the feed roll 2'. This leads to a simplification of the driving mechanism.

EXAMPLE V On the apparatus illustrated in FIG. 3, but provided with a stationary roll 4', a 210-filament nylon-6 yarn was drawn to a tire yarn having a denier of 1260. The circumferential speeds of the rolls 2'; 6, 7; and 12, 13 were, respectively, 400 meters per minute, 2000 meters per minute, and 2000 meters per minute. The roller pair 6, 7 was provided with a heating device, which heated the running surface of these rolls to 220 C. The rolls 4' and 12, 13 were not provided with a heating device. By an internally flowing cooling liquid the roll 4' was cooled to a temperature at the running surface of 100 C. The temperature of the running surface of the roll 2' was on an average 50 C. In this run the drawing neck was maintained at guide 11 by the controller 14.

The drawn yarn had a tenacity of 9.5 grams per denier, an elongation at break of 21% and a shrinkage in boiling water of 17%.

Although it seems rather unusual first to cool the yarn (on the roll 4') and then again to heat it (on the rolls 6, 7), the cooled roll 4' is yet found to give rise to fewer filament breaks than a non-cooled roll 4'.

What is claimed is:

1. A process for drawing a thermoplastic synthetic linear polymeric yarn which comprises feeding said yarn to a driven feed roll, passing the yarn from the feed roll to at least one rotary friction member over which the yarn slips, controlling the tensile force applied to said yarn as it slips over said rotary frictional member, and passing the yarn to a draw roll driven at a circumferential speed higher than the circumferential speed of said feed roll whereby the yarn is subjected to a first draw before contacting the rotary friction member and to a second draw after contacting the rotary friction member and then discharging the drawn yarn from said draw roll, said first draw being localized by sensing the increase in temperature due to heat being liberated at the drawing neck of said yarn and manipulating one or more process parameters affecting the drawing neck.

2. The process of claim 1 in which the first draw begins on said feed roll.

References Cited UNITED STATES PATENTS 3,018,610 1/1962 Kleinekathofer 26468 X 3,342,975 9/1967 Carr 34-448 X 3,457,338 7/1969 LeFavre 264290 FOREIGN PATENTS 781,105 3/1968 Canada 264290' 964,369 7/1964 Great Britain 264290 PHILIP E. ANDERSON, Primary Examiner US. Cl. X.R.

181; 16l172, 402; 264-68, 210 F, 290 N, 290 T, DIG 56 

